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Transcript of Protein Synthesis Chapter 17. Protein synthesis DNA Responsible for hereditary information DNA...
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Protein Synthesis
Chapter 17
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Protein synthesis
DNA Responsible for hereditary information DNA divided into genes Gene: Sequence of nucleotides Determines amino acid sequence in
proteins Genes provide information to make
proteins
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Protein synthesis
DNA RNA protein
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Central Dogma
Mechanism of reading & expressing genes
Information passes from the genes (DNA) to an RNA copy
Directs sequence of amino acids to make proteins
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Protein synthesis
Transcription: DNA sequence is copied into an RNA Translation: Information from the RNA is turned
into an amino acid sequence
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RNA
RNA (ribonucleic acid) Single strand Sugar –ribose (-OH on 2’ carbon) Uracil instead of thymine
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RNA
mRNA: Messenger RNA Transcribes information from DNA Codons (3 nucleotides) CGU mRNA Codes for amino acids rRNA: Ribosomal RNA Polypeptides are assembled
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RNA
tRNA: Transfer RNA Transports aa to build proteins Positions aa on rRNA Anticodons (3 complementary nucleotides) GCA
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Cracking the code
Francis Crick Codons (Triplet code)-mRNA Each codon corresponds to an aa 20 amino acids Reading frame Reading symbols in correct
groupings
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Cracking the code
1 or 2 deletions or additions Gene was transcribed incorrectly 3 deletions Reading frame would shift Gene was transcribed correctly
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WHYDIDTHEREDCATEATTHEFATRAT
WHYIDTHEREDCATEATTHEFATRAT
WHYDTHEREDCATEATTHEFATRAT
WHYTHEREDCATEATTHEFATRAT
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The code
Universal code AGA codes for amino acid Arginine Humans & bacteria Genes from humans can be
transcribed by mRNA from bacteria Produce human proteins Insulin
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Protein synthesis
DNA RNA Protein
Transcription Translation
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Prokaryotes
Transcription Getting the code from DNA Template strand Strand of DNA that is transcribed or
read Transcribed RNA is complementary
to the DNA
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Prokaryotes
Coding strand DNA strand not coded Same sequence of nucleotides as
the RNA transcript Only T instead of U.
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Prokaryotes
RNA polymerase Enzyme Adds nucleotides to the 3’end 5’to3’ direction Does not need a primer to start
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Prokaryotes
Stages of transcription Initiation Elongation Termination
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Prokaryotes
Initiation Promoters: Sequence on DNA where
transcription starts -35 sequence TTGACA -10 sequence TATAAT Sequences are not transcribed
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Prokaryotes
RNA polymerase binds promoter Unwinds DNA Uses an ATP or GTP to start Uses phosphate group Transcription bubble: RNA polymerase, DNA & growing
RNA strand
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Prokaryotes
Termination Stop signal Sequence on DNA RNA transcript signals polymerase
to detach from DNA RNA strand separates from the DNA
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Prokaryotes
Translation Passing the code to make a
polypeptide mRNA binds to rRNA on the
ribosome mRNA attaches so only one codon is
exposed at a time
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Ribosome
Located in the cytoplasm Site of translation 2 subunits composed of protein &
RNA Small (20 proteins and 1 RNA) Large (30 proteins and 2 RNA) 3 sites on ribosome surface involved
in protein synthesis E, P, and A sites
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Ribosome
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Ribosome
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Prokaryotes
tRNA (anti-codon) Complementary sequence Binds to mRNA tRNA carries a specific amino acid Adds to growing polypeptide 45 tRNA’s
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Prokaryotes
Aminoacyl-t-RNA synthetases Activating enzymes Link correct tRNA code to correct aa One for each 20 amino acids Some read one code, some read
several codes
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Prokaryotes
Nonsense codes UAA, UAG, UGA code to stop AUG codes for start as well as
methionine Ribosome starts at the first AUG it
comes across in the code
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Prokaryotes
Translation 1. Initiation 2. Elongation 3. Termination
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Prokaryotes
Initiation Initiation complex 1. tRNA with formylmethionine attached
binds to a small ribosome 2. Initiation factors position the tRNA on
the P site 3. A site (aminoacyl) where other tRNA’s
form
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Prokaryotes
4. tRNA is positioned on to the mRNA at AUG
5. Attachment of large ribosomal unit
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Prokaryotes
Elongation factors Help second tRNA bind to the A-site Two amino acids bind (peptide
bond) Translocation: Ribosome moves 3 more
nucleotides along mRNA in the 5’to 3’ direction
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Prokaryotes
Initial tRNA moves to E site Released New tRNA moves into A site Continues to add more aa to form
the polypeptide
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Prokaryotes
Release factors: Proteins that release newly made
polypeptides Codon (UAG, UAA, UGA) Release factor binds to the codon Polypeptide chain is released from A
site
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Eukaryotes
Transcription (nucleus) Initiation Elongation Termination
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Eukaryotes
Initiation Transcription Initiation Complex
is formed Transcription factors bind first to the
promoter RNA pol II binds DNA Starts to transcribe
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Fig. 17-7b
Elongation
RNApolymerase
Nontemplatestrand of DNA
RNA nucleotides
3 end
Direction oftranscription(“downstream”) Template
strand of DNA
Newly madeRNA
3
5
5
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Fig. 17-UN1
Transcription unit
Promoter
RNA transcriptRNA polymerase
Template strandof DNA
5
553
3 3
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Eukaryotes
Termination Polyadenylation signal sequence Recognized by RNA polymerase II mRNA is released
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Transcription
D:\Chapter_17\A_PowerPoint_Lectures\17_Lecture_Presentation\1707TranscriptionIntroA.html
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Eukaryotes
mRNA is modified Nucleus RNA processing
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Eukaryotes
5’ cap Addition of a GTP 5’ phosphate of the first base of
mRNA Methyl group is added to the GTP 3’poly-A-tail Several A’s on the end of the mRNA
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Eukaryotes
Introns: non-coding sequences of nucleic
acids Exons: coding sequences of nucleic acids
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Euraryotes
RNA splicing Cut out introns Reconnect exons snRNP’s (small nuclear RNA’s) Spliceosome: Many snRNP’s come together &
remove introns
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Eukaryotes
Translation 1. Initiating aa is methionine 2. Initiation complex is more
detailed
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Fig. 17-16bP site (Peptidyl-tRNAbinding site) A site (Aminoacyl-
tRNA binding site)E site(Exit site)
mRNAbinding site
Largesubunit
Smallsubunit
(b) Schematic model showing binding sites
Next amino acidto be added topolypeptide chain
Amino end Growing polypeptide
mRNAtRNA
E P A
E
Codons
(c) Schematic model with mRNA and tRNA
5
3
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<>
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Fig. 17-UN3
mRNA Ribosome
Polypeptide
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<>
D:\Chapter_17\A_PowerPoint_Lectures\17_Lecture_Presentation\1718TranslationIntroA.html
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Similarities
DNA RNA Protein
Transcription Translation
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Differences in gene expression
Transcription 1. Prokaryotes one RNA polymerase Eukaryotes 3 RNA polymerases (poli-II
mRNA synthesis) 2. Prokaryotes mRNA contain transcripts
of several genes Eukaryotes only one gene 3. Prokaryotes no nucleus so start
translation before transcription is done
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Differences in gene expression
3. Eukaryotes complete transcription before leaving the nucleus
4. Eukaryotes modify RNA Introns/exons
5. Prokaryotes Polymerase binds promoters
Eukaryotes transcription factors bind first then enzyme
6. Termination
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Differences in gene expression
Translation 1. Prokaryotes start translation with
AUG Eukaryotes 5’cap initiates
translation 2. Prokaryotes smaller ribosomes
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Mutations
Changes in genetic information Point mutations: Change in a single base pair Sickle cell mutation
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Mutations
Two types 1. Base-pair substitution Exchange one nucleotide and base
pair with another Silent mutations No effect on proteins
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Mutations
Missense mutations: Substitutions that change one aa for
another Little effect
![Page 83: Protein Synthesis Chapter 17. Protein synthesis DNA Responsible for hereditary information DNA divided into genes Gene: Sequence of nucleotides.](https://reader033.fdocuments.in/reader033/viewer/2022051316/56649f525503460f94c7646a/html5/thumbnails/83.jpg)
Mutations
Nonsense mutations Point mutation codes for stop codon Stops translation too soon Shortens protein Non-functional proteins
![Page 84: Protein Synthesis Chapter 17. Protein synthesis DNA Responsible for hereditary information DNA divided into genes Gene: Sequence of nucleotides.](https://reader033.fdocuments.in/reader033/viewer/2022051316/56649f525503460f94c7646a/html5/thumbnails/84.jpg)
Mutations
2. Insertions or deletions Additions or losses of nucleotides Frameshift mutations Improperly grouped codons Nonfuctional proteins
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Fig. 17-23Wild-type
3DNA template strand
5
5
53
3
Stop
Carboxyl endAmino end
Protein
mRNA
33
3
55
5
A instead of G
U instead of C
Silent (no effect on amino acid sequence)
Stop
T instead of C
33
3
55
5
A instead of G
Stop
Missense
A instead of T
U instead of A
33
3
5
5
5
Stop
Nonsense No frameshift, but one amino acid missing (3 base-pair deletion)
Frameshift causing extensive missense (1 base-pair deletion)
Frameshift causing immediate nonsense (1 base-pair insertion)
5
5
533
3
Stop
missing
missing
3
3
3
5
55
missing
missing
Stop
5
5533
3
Extra U
Extra A
(a) Base-pair substitution (b) Base-pair insertion or deletion
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Mutagens
Chemical or physical agents Mutations in DNA